1 FIELD OF THE INVENTION
The present invention relates to a waveguidemounted amplifier having an active element arranged in a waveguide.
2. DESCRIPTION OF THE PRIOR ART
There has been devised and demonstrated an amplifier circuit for amplifying signals in an SHF band fabricated by thin film circuit techniques or thick film circuit techniques. Furthermore, amplifier circuits or oscillator circuits of the type in which semiconductor devices are arranged within a waveguide have been widely used. For instance, the amplifier circuits of the type in which a GaAs-FET is incorporated in a waveguide are well known in the prior art, but they can handle only low power and their uses are limited to the front-end amplifier.
In the case of an SHF-band amplifier fabricated by film circuit techniques, such passive elements as inductors, capacitors and lead wires are fabricated by using conductive metal layers formed on an insulating substrate. There is a considerable amount of radiation from these passive elements at high frequencies, i.e., in the SHF band and they accordingly cause problems of radiation losses. Furthermore, dielectric losses inherent to dielectric components at high-frequencies cannot be ignored and thus they cause problems of dielectric losses. Moreover, parasitic oscillation may frequently occur when the amplifier gain in each stage increases. In addition, the output response to the input signal is degraded by mutual coupling between the input and output signals due to radiation.
However, when a circuit is increased in size in order to eliminate such parasitic oscillation and mutual interference, power losses may increase. Therefore, both high gain and high stability have been extremely difficult to achieve while minimizing the losses.
FIGS. 1A and 1B show, one example of the prior art waveguide including a mounted diode. Here, a diode 13 is incorporated in a waveguide 11, and a voltage is applied to the diode 13 through a feeder 12 and the electromagnetic waves are radiated from part of the feeder 12 to travel through the waveguide 11. A short plunger 14 is provided to match the waveguide characteristic impedance with the desired value. However, this concept of incorporating diode 13 into waveguide 11 cannot directly be applied to realization of a waveguide-mounted amplifier wherein one or more three-terminal devices including GaAs-FETs are incorporated into a waveguide because diode 13 cannot be used as a three-terminal device for amplification.
Meanwhile, Japanese Utility Model Application No. 56-74482, filed May 25, 1981 (Laid-open No. 57-188401, laid open Nov. 30, 1982) discloses a microwave circuit in which, as shown in FIGS. 2A and 2B, waveguide 21 provides ridges 22 to match the waveguide impedance with the specified value at the point where device 23 is mounted. Input power is applied to GaAs-FET 23 which is fastened to ridges 22 and is amplified so that electromagnetic waves are radiated from waveguide 21.
Since, however, such a microwave circuit as shown in FIGS. 2A and 2B employs ridges 22, mentioned heretofore the electromagnetic-wave modes input to and output from GaAs-FET 23, used as an active device, through waveguide 21 and ridges 22 are converted in the interior of waveguide 21. Thus, ridges 22 must be long. This results in a microwave circuit of large size. In addition, losses are caused by mode conversion.
Furthermore, such a microwave circuit as shown in FIGS. 2A and 2B is proposed to be used for a front-end of each amplifier circuit. Therefore, even though NF is satisfactorily low with wide frequency band in each amplifier, the amplifier gain cannot be increased beyond a certain limit because the input and the output ports are not separated from each other.
For instance, H. Matsumura reported at the National Convention sponsored by The Institute of Electronics and Communication Engineers of Japan held in 1982 (The National Convention Record, No. 789) that two amplifier elements were serially connected in two stages so that the gain of 6 dB (at 14 GHz) was attained. However, the circuit is constructed in a limited use only to form a front-end amplifier. That is, if this type circuit is employed to construct a power amplifier circuit with a high gain, parasitic oscillation may occur due to bypassed input-to-output interaction. It results, therefore, in the necessity of providing separation means which is capable of separating the output from the input.
In the MTT symposium sponsored by the IEEE held in 1978, C. F. Krumm proposed in his article on "A 30-GHz GaAs FET AMPLIFIER" (pp.383-385, Digest of Technical Papers) an amplifier circuit of the type in which electromagnetic waves are received directly from an input waveguide and, are fed to an output waveguide after being amplified with a built-in active device. The amplifier circuit shown in FIG. 3 handles electromagnetic waves within waveguides 31 and 32 when operating for amplification, and thus the electromagnetic waves are amplified within the interior of the waveguides. But, input and output waveguides 31 and 32 are in the L-form and FET mount 33 is substantially arranged out of waveguides 31 and 32. Therefore, this type of circuit is attributed to another category, not the same as the microwave circuit disclosed in Japanese Utility Model Application No. 56-74482.
In the amplifier circuit shown in FIG. 3, two waveguides 31 and 32 are arranged in an opposed relationship and the respective ends which face to GaAs-FET mount 33 are bent upright so that waveguides 31 and 32 are L-shaped. A rim 33 mates with the upright open ends of waveguides 31 and 32, and is located on the open ends of waveguides 31 and 32 so as to bridge therebetween. That is; rim 33 has a pair of apertures aligned with the open ends of waveguides 31 and 32, and separated from each other by arm 34. Arm 34 has groove 35 in which a GaAs-FET 36 is arranged. A cover plate 37 covers rim 33. However, the positional relationship between waveguides 31 and 32, and GaAs-FET 36 is discontinuous and thus an increased gain-and-bandwidth product is difficult for this type of amplifier.